Login-free option for tutorials

[dtkaplan]

Provide an alternative to authorize_submissions() that doesn't require a login. This might be useful for tutorials distributed as part of a package and with local storage of the submissions.

Need to establish whether local storage works for tutorials run from a package.

[dtkaplan]

This is included as of Apr 2. Submissions are recorded with an "Unauthorized [user name]" credential, where "user name" is whatever (including nothing) the user entered in the ID box.